Tubular prostheses commonly known as stents have been used to reinforce and strengthen damaged blood vessels and other body passages. For example, the blood vessels can collapse, dilate, become partially occluded or otherwise damaged by disease or other causes. The presence of an aneurysm or stricture in the blood vessel often requires implantation of a stent to strengthen the vascular wall in the area of the damage. Other passages in the body can also sometimes benefit from stent implantation, including the esophagus, the trachea, the gastro intestinal tract, the bile duct, the ureter and the urethra.
The benefits of self-expanding stents have been recognized. A self-expanding stent is held in a contracted state until it has been positioned properly, typically with the aid of an instrument such as a catheter. After the stent has been placed properly in the damaged blood vessel, it is allowed to expand against the damaged vessel wall in order to reinforce the damaged area. Examples of self-expanding stents are disclosed in Burton et al. U.S. Pat. Nos. 5,026,377 and 5,078,720, Hillstead U.S. Pat. No. 5,019,085, Wiktor U.S. Pat. No. 4,969,458 and Gianturco U.S. Pat. No. 5,041,126. The Wicktor and Gianturco stents are in the form of coiled or looped wires that are unable to contact the entirety of the weakened vessel wall. The same is true of the Hillstead stent which takes the form of a multiple loop wire structure. The stents disclosed in the two Burton patents are braided structures that are likewise incapable of contacting the entirety of the damaged vessel wall. All of the stents and particularly their placement means are complicated to construct, and the stents are difficult to place precisely in the damaged vessel.